The subject matter disclosed herein relates generally to fuel injectors for gas turbine engines and more particularly to a fuel injector assembly.
Gas turbine engines, such as those used to power modern aircraft, to power sea vessels, to generate electrical power, and in industrial applications, include a compressor for pressurizing a supply of air, a combustor for burning a hydrocarbon fuel in the presence of the pressurized air, and a turbine for extracting energy from the resultant combustion gases. Generally, the compressor, combustor, and turbine are disposed about a central engine axis with the compressor disposed axially upstream or forward of the combustor and the turbine disposed axially downstream of the combustor. In operation of a gas turbine engine, fuel is injected into and combusted in the combustor with compressed air from the compressor thereby generating high-temperature combustion exhaust gases, which pass through the turbine and produce rotational shaft power. The shaft power is used to drive a compressor to provide air to the combustion process to generate the high energy gases. Additionally, the shaft power is used to, for example, drive a generator for producing electricity, or drive a fan to produce high momentum gases for producing thrust.
An exemplary combustor features an annular combustion chamber defined between a radially inboard liner and a radially outboard liner extending aft from a forward bulkhead. The radially outboard liner extends circumferentially about and is radially spaced from the inboard liner, with the combustion chamber extending fore to aft therebetween. A plurality of circumferentially distributed fuel injectors are mounted in the forward bulkhead and project into the forward end of the annular combustion chamber to supply the fuel to be combusted. Air swirlers proximate to the fuel injectors impart a swirl to inlet air entering the forward end of the combustion chamber at the bulkhead to provide rapid mixing of the fuel and inlet air.
Combustion of the hydrocarbon fuel in air in gas turbine engines inevitably produces emissions, such as oxides of nitrogen (NOx), which are delivered into the atmosphere in the exhaust gases from the gas turbine engine. In order to meet regulatory and customer requirements, engine manufacturers strive to minimize NOx emissions. An approach for achieving low NOx emissions makes use of a rich burning mixture in the combustor front end at high power. Such rich burning requires good mixing of fuel and air to control smoke at high power. The fuel injector must also provide a good fuel spray at low power for ignition, stability, and reduced emissions.
One solution for accommodating both high power and low power operations is the use of a conventional airblast fuel injector with an axial inflow swirler down the center of the fuel nozzle with radial inflow swirlers mounted to the tip of the fuel injector at the downstream end of the fuel nozzle. Having the radial inflow swirlers mounted to the tip of the fuel injector increases the size of the fuel injector, requiring more space in the dump gap between the diffuser and combustor in order to install and remove the fuel injector, which increases engine weight and cost. In addition, having the radial inflow swirlers mounted to the tip of the fuel injector makes the fuel injector heavier, which requires a thicker and heaver stem to support the fuel injector and minimize vibrations, thereby increasing the weight and cost of the fuel injector.
Another solution for accommodating both high power and low power operations is the use of a duplex fuel injector having a fuel nozzle surrounded by high shear air swirlers. The fuel nozzle of the fuel injector includes a primary pressure atomizing spray nozzle to provide an adequate fine primary fuel spray for ignition since, at ignition, there may be inadequate airflow shear to sufficiently atomize the fuel for reliable operation. This primary atomizing spray nozzle requires a valve at the base of the fuel injector to control flow between the primary and secondary fuel passages. So although the duplex fuel injector is lighter than the conventional airblast fuel injector having radial inflow swirlers mounted to the tip of the fuel injector eliminating some of the issues referenced previously, the external valve required by the duplex fuel injector increases the cost while reducing reliability of the duplex fuel injector.